This invention relates to an exhaust gas control device that is suitable for use in motorcycles.
It is well known that the performance of an internal combustion engine is effected significantly by the design and configuration of the exhaust system. Furthermore, it is also known that conventional exhaust systems which may be tuned to increase high speed performance, tend to reduce the performance under other running conditions. For example, it is known that the output of an internal combustion engine can be improved if the engine is provided with a plurality of exhaust pipes for each cylinder or exhaust port of the engine and which all merge into a common expansion chamber. The exhaust gases are then discharged to the atmosphere from this expansion chamber. Although this type of system can significantly increase high speed performance, it has also been found to deteriorate the performance at mid ranges. The resulting engine output provides an unsatisfactory dip in the mid range torque curve of the engine.
It has been recognized that the exhaust system can be made adjustable so as to increase its performance under all running conditions through the use of a reflective valve member that is positioned in the expansion chamber in confronting relationship with the exhaust pipes. By appropriately adjusting the effective flow areas of the exhaust pipes, the dip in mid range performance can be substantially eliminated. This is because the valve member causes the reflection of exhaust pulses back to the exhaust port which can improve rather than deteriorate scavenging and performance. Although this type of arrangement has particular utility, there are certain disadvantages and difficulties in applying it to actual practice.
The practical application of this principal is particularly difficult in connection with compact vehicles such as motorcycles. In conjunction with a motorcycle application, it is the normal practice to place the expansion chamber and exhaust control valve beneath the engine transmission assembly. The exhaust pipes then run from the cylinders of the engine down to the expansion chamber. However, it is desirable to insure that the expansion chamber has sufficient volume so as to improve the high speed performance of the engine and its low positioning in the motorcycle can adversely effect performance, such as the leaning of the motorcycle when cornering.
It is, therefore, desirable to provide a relatively compact transversely extending expansion chamber that can achieve the desired results. However, the configuration of such expansion chambers can give rise to problems in manufacturing. This is particularly true if it is attempted to form the expansion chamber and the associated exhaust gas control valves and the inlets to the expansion chamber from a single piece casting. Such castings are extremely complicated and because of this it is difficult to control the actual configuration of the device. It has, therefore, been proposed to provide an arrangement wherein the expansion chamber and valve assembly is at least partially fabricated. Such an arrangement is shown in Japanese published application No. 61-157999, dated July 7, 1986. In conjunction with forming such an expansion chamber and valve arrangement it is desirable to insure that the individual exhaust pipes are separated from each other and do not communicate with each other until they enter the expansion chamber and that this individual relationship extend up until the point at which the valve member is disposed. However, the construction shown in that Japanese application is extremely difficult to fabricate and many of the welds may become broken and cause the exhaust gases to communicate with each other upstream of the exhaust valve and render the device less effective.
It is, therefore, a principal object of this invention to provide an improved fabricated exhaust control device for a vehicle.
It is a further object of this invention to provide an improved fabricated exhaust control device which may be easily manufactured and which will be reliable in long term operation.
In connection with the use of such exhaust control devices, there is a further disadvantage to forming them as castings. Because of the large weight and mass of a casting, the applicability to lightweight vehicles is severely limited. Furthermore, the mass of the casting can give rise to a resonant effect which can provide objectionable noise.
It is, therefore, yet another object of this invention to provide an improved and simplified arrangement for fabricating an exhaust control device of the type described.
In connection with these types of exhaust control devices, it is desirable to provide, as aforenoted, a relatively low height and a relatively shallow width. If the exhaust pipes which enter the exhaust control device are round, as is typical practice, this tends to unduly extend the width of the unit. Therefore, it is proposed to employ an arrangement wherein the inlets for the exhaust control device are configured so that they start in a round shape to mate with the exhaust pipes and then merge into a rectangular shape so as to permit a more compact construction without increasing unduly the width or size of the device.
The use of such transitional pieces and the formation of a fabricated exhaust control device presents obvious problems.
It is, therefore, yet a further object of this invention to provide an improved fabricated exhaust control device wherein the inlet sections provide a transition from a cylindrical cross section to a rectangular cross section and a simple compact and easily fabricated arrangement is achieved.